Apparatus for detecting anomalies in pipes

ABSTRACT

An apparatus and method for detecting anomalies in ferrous pipe structures is presented. An electrical current is passed through the ferrous pipe structure so as to create a magnetic field in the pipe. A sensor having one or more sensor shoe members is placed in the interior of a ferrous pipe structure to be inspected. Each sensor shoe member has one or more magnetometer elements for detecting the magnetic fields in the region of the ferrous pipe structure adjacent to which the sensor shoe member is placed.

This is a division of application Ser. No. 08/241,031, filed 10 May 94,now U.S. Pat. No. 5,479,100.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of apparatus and methods fordetecting anomalies in ferrous pipe structures, such as natural gas oroil pipelines, through the use of magnetic sensors which are passedalong the interior of the pipe structures.

2. The Prior Art

Piping systems, such as natural gas or oil piping systems, need to beinspected, after construction, and periodically after use has begun, forthe purposes of detecting defects or points of failure or leakage, or insome cases, predicting such points of failure or leakage. Since suchpipelines are typically buried or submerged, it has become necessary todevelop a means for inspecting such pipe structures using preprogrammedrobotic or remotely operated or teleoperated devices.

It is known, for example, that in ferrous pipe structures, such as areused for natural gas or petroleum, the pipe will have a residual orremnant magnetic field associated with it, which can be detected andmeasured by appropriate electromagnetic sensors placed next to oragainst the pipe structure. It is also known that by placing magneticfield sources next to such pipe structures, a portion of the magneticflux from the sources can be forced to travel through the pipestructure. When sensors are activated to seek the imposed field(s;)passing through a pipe structure, if the particular local section ofpipe is without welds, flaws or other anomalies, then the imposed fieldswill not be detected. If, however, the local section of pipe has welds,cracks, or other flaws or anomalies, then the imposed field will "leak"from the anomaly and be detected by the sensors, when the leakage fieldis compared to the profile of the residual or remnant field detected andmeasured for the same local portion of pipe.

Numerous examples of anomaly detection devices, using magnetic fieldgenerators and magnetic field sensor, exist in the prior art, includingsuch devices as are disclosed in Beaver et al., U.S. Pat. No. 3,460,028;Barton, U.S. Pat. No. 3,593,122; Smith, U.S. Pat. No. 4,105,972; Birchaket al., U.S. Pat. No. 4,649,343; Ando et al., U.S. Pat. No. 4,742,298;and Cecco et al , U.S. Pat. No. 4,855,676.

The Beaver et al. '028 reference shows an anomaly detector having asingle axially oriented magnetic field generating apparatus centrallyarranged within the sensor rig. Annular brushes positioned fore and aftof a plurality of magnetic field sensor "sledges" on the sensor rigconvey the magnetic field into and out of the pipe structure, such thatthe magnetic flux lines are parallel to the longitudinal axis of thepipe structure. The "sledges" are held in spring-biased relation againstthe interior surface of the pipe structure, as the sensor rig movesalong the interior of the pipe structure.

The apparatus of the Barton '122 patent likewise employs fore and aftmagnetic pole pieces to establish an axially extending magnetic fluxpath, with sensor "shoes" positioned axially between the pole pieces. Anadditional pole piece, positioned aft of the paired pole pieces, andhaving brush parts inclined relative to the interior surface of the pipestructure acts to strengthen the residual magnetic field in the pipestructure. The residual fields detected are compared to the readingstaken when the pipe structure has the active magnetic field imposed uponit. The discrepancies in the two sets of readings indicates the presenceof anomalies, which may be welds, or actual flaws in the pipe structure.

The Smith '972 patent shows a pipeline inspection vehicle having aplurality of sensor heads arranged in a circle about the vehicle, andheld in place against the interior surface of the pipe structure by anannular, spring-biased structure. Each individual sensor head may havemagnetic field generating apparatus therein, as well as magnetic fieldsensing apparatus.

The Birchak et al. '343 patent describes an inspection system for use insmall bore tubes, in which a scanner body has two annular magneticcores, arranged perpendicular to one another, inside a hollow core ofthe scanner body. An array of magnetic field sensors are arrangedcircumferentially around the scanner body. The field generated by thetwo magnetic cores, simultaneously, may be manipulated by phase shiftingand amplitude variations, so as to shift the direction of the field,even to producing a helical magnetic flux, or to swing the flux throughnearly 180° to expose an anomaly to magnetic flux directed normal to it.

The apparatus of the Ando et al. '298 patent employs an axiallyextending primary magnetic coil, and a plurality of circumferentiallyextending secondary coils positioned radially outwardly of the primarycoil. The secondary coils do not impose a magnetic field, but rathersense the axial component of the magnetic flux generated by the primarycoil, in the form of a voltage imposed on the secondary coil. The sensedcomponent changes in the presence of a flaw positioned between the polesof the primary coil.

The Cecco et al. '676 reference shows an apparatus for inspection of apipe, having a sensor member configured to produce both axiallyextending and radially extending magnetic fields, positioned along thelength of the sensor member. The Cecco et al. reference describes thatboth fields are of such strength as to obtain very high levels ofsaturation in the pipe structure.

The present invention is particularly directed to inspection systems forferrous pipe structures, which are particularly suited to small borepipe structures, such as the piping systems for natural gasdistribution, the pipes of which typically have a nominal four-inchinterior diameter. Commonly, prior art defect detection systems, whichhave typically been configured for much larger diameter pipes, haverelied upon detection techniques involving the complete saturation ofthe pipe structure by the generated magnetic fields. Such saturationinvolves substantial power consumption by electromagnets, or the use oflarge, typically heavy, permanent magnets.

To provide support, such as power cables and transformers orsufficiently powerful and durable portable power supplies forelectromagnets, and/or conveyance mechanisms for the sensors forsaturation-type detector devices, in the confined environment of asmall-bore detector device, is a difficult task-. It is desirable,therefore, to provide a way of avoiding the logistical difficultiespresented by saturation-type detector systems.

Particular problems are presented by anomalies which are closer to theoutside surface of the pipe structure, such as cracks beginning from theoutside, toward the interior of the pipe. As mentioned, due to spacerequirements, the power of the magnetic field generating means which canbe carried on board the sensor is limited. Further, while themagnetometers which are carried on the sensor, are often carried inshoes which are held in a spring or mechanically biased manner againstthe inner surface of the pipe structure, there will still be an"air-gap" between the surface of the shoe and the pipe interior surface,across which the magnetic fields must jump to reach the pipe from thegenerators and return to the magnetometers. This gap, which may be onlya few thousandths of an inch, is still enough to cause substantialattrition in the strength of the field being imposed upon the pipe, andsubsequently being detected by the magnetometers.

An even more important potential problem is that the interior surfacesof gas pipes can be relatively irregular, with numerous bumps andridges. This irregular surface forms part of the magnetic field circuit,causing variations in the emitted and sensed magnetic field. Theirregularities thus become a source of error in the observedfluctuations of the magnetic field, as the sensor shoes pass over theinterior surface of the pipe.

It is desirable, therefore, to provide a way of imposing a magneticfield into a pipe structure, without requiring large or complicatedmagnetic field generating devices to be carried by the sensor.

It is also desirable to provide a way of imposing a magnetic field intoa pipe structure, which is suitable for use with sensors which are sizedfor small pipe diameter applications.

SUMMARY OF THE INVENTION

The invention is directed to an apparatus for detecting anomalies in aferrous pipe structure, which comprises, in part, sensor means, forpositioning within and movement along an interior of the ferrous pipestructure; means, operably associated with the sensor means, forimposing one or more magnetic fields into the ferrous pipe structure,the means for imposing one or more magnetic fields being operablydisposed substantially externally to the pipe structure; means, operablyassociated with the sensor means, for detecting magnetic fieldsemanating from the ferrous pipe structure whether due to remnantinduction in the ferrous pipe structure or to magnetic fields imposed bythe means to impose magnetic fields; means for generating data signalscorresponding to the magnetic fields detected by the means to detectmagnetic fields; control means for receiving and processing the datasignals generated by the sensor means, and for converting the datasignals into information from which a user may determine the presenceand characteristics of anomalies in the ferrous pipe structure; meansfor communicating the data signals generated by the sensor means to thecontrol means; and means for propelling the sensor means along theinterior of the ferrous pipe structure.

The means to impose magnetic fields comprises means for causing anelectrical current to be passed through the ferrous pipe structure, soas to create a magnetic field in the pipe structure. In addition, thesensor means comprises a sensor support frame; at least one sensor shoemember, operably configured to be placed adjacent to an interior surfaceof the ferrous pipe structure; and means for operably positioning the atleast one sensor shoe member adjacent to the interior surface of theferrous pipe structure.

The means to detect magnetic fields in the ferrous pipe structurecomprises at least one magnetometer operably disposed in the sensor shoemember, so as to detect magnetic fields emanating from the ferrous pipestructure.

The means for communicating the data signals generated by the sensormeans to the control means comprises a hardwire connection from thesensor means to the control means. In an alternative embodiment of theinvention, the means for communicating the data signals generated by thesensor means to the control means comprises telemetry means operablyassociated with the sensor means and the control means for transmittingthe data signals from the sensor means to the control means without ahardwire connection therebetween. In a still further preferredembodiment of the invention, they comprise means for recording the datasignals generated by the sensor means, for playback into the controlmeans after retrieval of the sensor means from the interior of theferrous pipe structure.

The invention also comprises a method for detecting anomalies in aferrous pipe structure, of the kind employing an apparatus including asensor to be positioned in and propelled along the interior of theferrous pipe structure wherein the sensor includes at least one sensorshoe member, including the steps of a) placing the at least one sensorshoe member within the interior of the ferrous pipe structure at adesired location to be inspected; b) measuring any present remnantmagnetic field within the ferrous pipe structure; c) imposing a firstmagnetic field, from an external source, onto the ferrous pipe structureand simultaneously measuring any magnetic field emanating from theferrous pipe structure; d) imposing a second magnetic field of reversedpolarity onto the ferrous pipe structure with the external source andsimultaneously measuring any magnetic field emanating from the ferrouspipe structure; e) comparing the remnant magnetic field measured withthe magnetic fields measured after imposition of the first, second,third and fourth magnetic fields to yield data representative ofanomalies in the ferrous pipe structure at the desired location.

The steps of imposing a first magnetic field, from an external source,onto the ferrous pipe structure and simultaneously measuring anymagnetic field emanating from the ferrous pipe structure; and imposing asecond magnetic field of reversed polarity onto the ferrous pipestructure with the external source and simultaneously measuring anymagnetic field emanating from the ferrous pipe structure, furthercomprise the steps of: a) providing a source of electrical current; b)connecting the source of electrical current to the pipe structure, atpositions upstream and downstream from the desired location to beinspected; c) actuating the source of electrical current so as to causeelectrical current to pass along the pipe structure through the desiredlocation to be inspected; d) reversing the polarity of the source ofelectrical current, relative to the pipe structure and actuating thesource of electrical current, so as to cause the current to flow inreverse direction through the pipe structure through the desiredlocation to be inspected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the apparatus for detecting anomalies in apipe structure according to the present invention; and

FIG. 2 is a side elevation, partially in section, of a sensor apparatusaccording to the present invention, shown with the sensor shoe membersdeployed against the inner surface of a pipe structure.

BEST MODE FOR CARRYING OUT THE INVENTION

While the present invention is susceptible of embodiment in manydifferent forms, there is shown in the drawings and will be describedherein in detail, one specific embodiment, with the understanding thatthe present disclosure is to be considered as an exemplification of theprinciples of the invention, and is not intended to limit the inventionto the embodiment illustrated.

FIG. 1 shows in schematic form, apparatus 10 for detecting anomalies inferrous pipe structures, such as pipe structure 12. Apparatus 10includes sensor 14, control computer 16, and a means for communicationbetween sensor 14 and control computer 16. Although such communicationmeans is shown in FIG. 1 as being represented by a hardwire connection18, other types of communication, such as by telemetry, or by placementof a data storage device (not shown) in sensor 14, among others, forlater playback of recorded data and downloading into control computer16, are also contemplated.

In addition, sensor 14 must be provided with some form of propulsionback and forth along the interior of pipe structure 12. Sensor 14 may bemoved by a push rod (not shown), examples of which are well known in theart, which may be externally controlled through breach 20 in pipestructure 12. Alternatively, sensor 14 may be attached to or constructedas part of a self-propelled robot crawler (not shown), examples of whichare already known in the art.

Sensor 14, shown in FIG. 2, includes sensor support frame 22 and sensorshoe members 24, 26. Sensor 14 may include a greater or lesser number ofsensor shoe members, and preferably should have as many as possiblearranged about the circumference of sensor 14, to provide as great acoverage of the surface of the pipe structure 12 as possible. Sensorshoe members 24, 26 are configured to be deployed from positions inpockets 28, 30, immediately adjacent to sensor support frame 22, to beheld in a resiliently biased manner against the inner surface 32 of pipestructure 12.

Deployment and maintenance of sensor shoe members 24, 26 against innersurface 32 can be obtained by pivotably supporting sensor shoe members24, 26 on arms 34, 36. Arms 34, 36 may be suitably biased, such as bysprings 38, 40, so as to Lend to press sensor shoe members 24, 26against inner surface 32. To retract arms 34, 36, a ballscrew mechanism42, of any suitable known configuration, may be provided, such that uponactuation and rotation of the screw 44, for example by an electricmotor, a ballnut 46 will be propelled axially in the direction of wings48, 50 of arms 34, 36. Ballnut 46 will drive an actuator member 47against wings 48, 50, causing arms 34, 36 to pivot about axes 52, 54,against the bias of springs 38, 40, thus withdrawing sensor shoe members24, 26 back into pockets 28, 30. The deployment and retraction of sensorshoe members 24, 26 may also be used when sensor 14 must pass obstaclesor restrictions in pipe structure 12.

Sensor support frame 22 of sensor 14 also provides space for theplacement and protection of various electronic circuitry, as furtherdiscussed hereinafter.

Each sensor shoe member, such as sensor shoe member 24, is provided witha magnetometer apparatus, which may be a Hall Effect apparatus, a coilmagnetometer, or, as in a preferred embodiment of the invention, afluxgate magnetometer, which provides the advantages of smaller spacerequirements, smaller power requirements, and greater sensitivity. Amulti-axis fluxgate magnetometer, such as a three-axis magnetometer,would be a preferred magnetic field sensor configuration, as it could beused to define the magnetic field as a resultant vector havingcomponents in each of three orthogonal coordinate axes.

In addition, each sensor shoe member may be provided with one or moremagnetic field sources, such as permanent magnets, or electromagnets.Such a combination of elements will enable detection of a wide varietyof anomalies in a pipe structure, particularly if the anomalies are onor near the inner surface of the pipe structure.

However, often the more significant, or more dangerous anomalies arecracks and hardspots which are in or near the outer surface of pipestructure. For example, if a crack has begun to propagate from the outersurface of the pipe structure, but has not breached the inner surface,the use of a combination of magnetic field sources and magnetometers, aspreviously described, may have some difficulty detecting the anomaly.There are several possible reasons for the difficulty.

Since there is no breach in the inner surface, the imposed magneticfield will only exit the pipe structure on the side of the breach, andthe flux will then turn and enter the pipe structure. Therefore, the"leakage" field which the sensors could "see" would have to passcompletely through the thickness of the pipe to be detected, and willpresent a rather weak signal. In addition, the use of sensor shoemembers, even though pressed against the inner surface of the pipestructure, still does not provide a perfect mode of imposing themagnetic field, inasmuch as there is always a finite "air-gap" betweenthe shoe member and the actual surface of the pipe.

The sensor shoes 24, in passing over the interior surface 32 of thepipe, pick up "noise" in the form of fluctuations in the imposed andmagnetic fields due to the irregular, though not necessarily flawed,interior surface 32. This "noise" creates errors in the processing ofthe readings which should be avoided if possible. The "air-gap" alsocauses an attrition of the power of the imposed magnetic field. AlthoughFIG. 2 is not intended to be to scale, it is accurate in that itreflects that while the sensor shoe members 24, 26 may appear, uponvisual inspection to be in direct contact with the inner surface of pipestructure 12, there is in reality a space or "air-gap" of some fewthousandths of an inch, which the magnetic fields being imposed and/orbeing sensed must cross, and that crossing takes power, which results indeterioration of the quality and detail of the readings obtained.

While it is not practical, in order to improve on the quality ofdetection of breaches and other anomalies which occur on the outersurface of the pipe structure, by using magnetometers on the outside ofthe pipe structure, a more powerful imposed magnetic field is desirable.To increase the power of the electromagnets would require larger andheavier cables and electromagnets, which would place an additionalburden on the actual sensor transport system, particularly in a smalldiameter pipe inspection system. Likewise, the alternate use of larger,heavier permanent magnets is also not practical.

One way to impose a magnetic field in the pipe structure, of almost anydesired flux strength, is to pass an electrical current through thepipe. Electrical current source 70, is shown in FIG. 1, schematically asan idealized source of current. The positive pole 72 is connected topipe structure 12 at a position I, to one side of an inspection regionII, and the negative pole 74 is connected to a position III, to theother side of inspection region II. Accordingly, the electrical"current" will flow in the direction of arrow C. In adherence to the"right-hand rule", a magnetic flux will be established which flowscircumferentially in the pipe structure 12. As seen by the viewer inFIG. 1, the (x)'s indicate magnetic flux into the pipe, while the (·)'sindicate magnetic flux out of the pipe. The use of applied electricalcurrent enables a very large magnetic flux to be created, which, in thecase of "external" anomalies in the pipe structure, facilitates theirdetection from within the bore of the pipe.

A magnetometer (not shown), for example a three-axis fluxgate-typemagnetometer, is part of a sensor package, which may be carried in eachsensor shoe member 24, 26. Appropriate circuitry for driving themagnetometer, and for taking the analog signals generated bymagnetometer, and converting them into digital data signals forprocessing by control computer 16, are located in sensor support frame22.

As mentioned, the use of electrical current being supplied through thepipe directly may be used as an alternative to, or in addition to,magnetic fields imposed from within the pipe structure, for example frommagnetic coils carried in the sensor shoe members. The internallycarried magnetic field generation means may be in the form of a singlecoil, or a pair of coils arranged at right angles to one another. Themagnetometer(s) may be positioned at the intersection of and between thepoles of the magnetic coils.

The procedure for inspection of a particular local section of pipestructure is as follows. The sensor 14 is placed in the desired localsection to be inspected. Sensor shoe members 24, 26 are in theirdeployed positions, against inner surface 32 of pipe structure 12. Themagnetometer(s) measure(s) and map(s) the residual/remnant field in thelocal region of the pipe structure. If a multi-axis magnetometer isused, the measurements may be resolved into vectors having components inthree orthogonal axes, for example, an X-axis, concentric with thelongitudinal axis of the pipe structure, and Y- and Z-axes being normalboth to the X-axis and each other.

The current source 70 is then actuated, in the configuration shown inFIG. 2, and a second set of readings are taken. If desired, the leadsmay be switched at source 70, and the source actuated again, so as toproduce a current in a direction opposite to the configuration shown inFIG. 2, with a third set of readings being taken.

The current may be manipulated in other ways as well. Alternating ordirect current may be used, which may produce distinct sorts ofreadings, for additional detail. In addition, the phase of alternatingcurrent may be varied, and direct current may be pulsed, to simulatealternating current. It is contemplated that currents of 10-20 ampereswill be used. Although this procedure is expected to be used while thepipe is "live" with ongoing flow of gas or oil, the procedure isbelieved to be entirely safe, due to the absence of any combustionoxygen or any opportunities for an open spark.

The readings from the magnetometer, as previously mentioned, whichtypically are in the form of analog electrical signals, may be convertedto digital data signals by an onboard analog-to-digital circuitry ofknown configuration, carried in central support portion 22 of sensor 14.This digital data may then be stored in an onboard recording device,such as digital memory, or may be immediately transmitted, via hardwire,or telemetry, if appropriate transmission circuitry is provided, (suchas indicated generally in phantom at 60, in FIG. 2) to control computer16. Once all the pertinent data for a particular inspection locationhave been recorded or transmitted, the sensor 14 may then be propelledto the next desired inspection location along pipe structure 12.

The data obtained by the inspection procedure may be processed through acomparison of the residual/remnant field readings at a particularinspection location, with the readings taken when the current(s) areflowing. Where defects or other anomalies occur, the superposition ofthe imposed fields upon the residual/remnant field can lead to knownparticular results which can suggest upon the type of anomaly which isfound. For example, in general, anomalies such as welds or hard spots(which are more likely sites of possible future failure) may havedifferent residual magnetism and a comparison of the residual andimposed fields is different than similar readings taken in the vicinityof, for example, cold worked regions, where the pipe may have beenaccidentally or intentionally bent, or dented, during installation.

The taking of measurements of residual and imposed fields, inparticular, using the powerful imposed fields provided through runningelectrical current directly through the pipe being inspected,facilitates the detection of anomalies which are on the outer regions ofthe pipe structure, anomalies which are more difficult to detect withlower powered fields imposed from within the interior of the pipe bymore conventional pipeline sensors.

The foregoing description and drawings merely explain and illustrate theinvention and the invention is not limited thereto except insofar as theappended claims are so limited, as those skilled in the art who have thedisclosure before them will be able to make modifications and variationstherein without departing from the scope of the invention.

What is claimed is:
 1. An apparatus for detecting anomalies in a ferrouspipe structure, comprising:sensor means for positioning within andmovement along an interior of the ferrous pipe structure; means operablyassociated with the sensor means for imposing one or more magneticfields into the ferrous pipe structure, the means for imposing one ormore magnetic fields being operably disposed substantially externally tothe pipe structure, and including means for applying an electricalcurrent directly to the pipe structure, so as to create a magnetic fieldin the ferrous pipe structure, said means for imposing one or moremagnetic fields includingmeans for imposing a first magnetic field, froman external source, onto the ferrous pipe structure and means forimposing a second magnetic field of reversed polarity relative to thefirst magnetic field, from an external source, onto the ferrous pipestructure; means operably associated with the sensor means for detectingmagnetic fields emanating from the ferrous pipe structure, whether dueto remnant induction in the ferrous pipe structure or to magnetic fieldsimposed by the means to impose magnetic fields; means for generatingdata signals corresponding to the magnetic fields detected by the meansto detect magnetic fields; control means for receiving and processingthe data signals generated by the sensor means, and for converting thedata signals into information from which a user may determine thepresence and characteristics of anomalies in the ferrous pipe structure,includingmeans for simultaneously measuring any magnetic fieldsemanating from the ferrous pipe structure as a result of an impositionof a magnetic field from the means for imposing a first magnetic field,from an external source, onto the ferrous pipe structure and means forsimultaneously measuring any magnetic fields emanating from the ferrouspipe structure as a result of an imposition of a magnetic field from themeans for imposing a second first magnetic field, from an externalsource, onto the ferrous pipe structure and means for comparing theremnant magnetic field measured with the magnetic fields measured afterimposition of first and second magnetic fields to yield datarepresentative of anomalies in the ferrous pipe structure at the desiredlocation; means for communicating the data signals generated by thesensor means to the control means; and means for propelling the sensormeans along the interior of the ferrous pipe structure.
 2. The apparatusfor detecting anomalies in a ferrous pipe structure according to claim1, wherein the sensor means comprises:a sensor support frame; at leastone sensor shoe member, operably configured to be placed adjacent to aninterior surface of the ferrous pipe structure; and means for operablypositioning the at least one sensor shoe member adjacent to the interiorsurface of the ferrous pipe structure.
 3. The apparatus for detectinganomalies in a ferrous pipe structure according to claim 2 wherein themeans for detecting magnetic fields emanating from the ferrous pipestructure comprises:a magnetometer operably disposed in the sensor shoemember, so as to detect magnetic fields emanating from the ferrous pipestructure.
 4. The apparatus for detecting anomalies in a ferrous pipestructure according to claim 1, wherein the means for communicating thedata signals generated by the sensor means to the control meanscomprises:a hardwire connection from the sensor means to the controlmeans.
 5. The apparatus for detecting anomalies in a ferrous pipestructure according to claim 1, wherein the means for communicating thedata signals generated by the sensor means to the control meanscomprises:telemetry means operably associated with the sensor means andthe control means for transmitting the data signals from the sensormeans to the control means without a hardwire connection therebetween.6. The apparatus for detecting anomalies in a ferrous pipe structureaccording to claim 1, wherein the means for communicating the datasignals generated by the sensor means to the control meanscomprises:means for recording the data signals generated by the sensormeans, for playback into the control means after retrieval of the sensormeans from the interior of the ferrous pipe structure.